Preparation and use of zirconia gels in the conversion of hydrocarbons



Patented June '8, 1948 PREPARATION AND USE OF ZIBCONIA GELS IN THECONVERSION OEJIYDROCARBONS Milton M. Mal-isle and Edward M. Grlest,Woodbury, N. J., assignors to Socony-Vacuum Oil Company, Incorporated, acorporation of New York No Drawing. Application March 16, 1944, SerialNo. 526,825

16 Claims. (Cl. 198-52) This invention relates to stable hydrogels ofzirconium oxide and to the porous products obtained by removal of watertherefrom. More particularly, the invention is concerned with a methodfor forming such hydrogels which is adapted to commercial practice. Thesubject matter of the present invention is related to that described inour copending application Serial No.

526,824, filed March 16, 1944.

Many inorganic hydrogels were prepared at an early date by dialysis ofaqueous sols prepared by hydrolysis of inorganic salts. This method isgenerally applicable to silica and metal oxides, but is not suited tocommercial production because the dialysis is extremely slow, requiringa period of weeks or months for relatively small batches. Thatdifliculty has been overcome in connection with some hydrogels, notablythat of silica, by formation of a hydrosol by mixing of suitable diluteaqueous solutions. At least one attempt has been made to apply the sametechnique to zirconia, but prior to this invention, the formation ofstable zirconia hydrogels capable of being washed and dried has not beenachieved.

It has been reported by C. B. Hurd et al., in Journal Am. Chem. 800.,64, 110-114 (1942), that zirconia hydrogel may be prepared by mixingsolutions of sodium salts and zirconyl chloride. The authors reportedthat the hydrogels prepared by mixing solutions of sodium acetate andzirconyl chloride reliquefied on standing at room temperature, whilehydrogels formed from sodium carbonate and zirconyl chloride reliquefiedat temperatures above 90 C. Finally, they conclude that zirconiahydrogels are soft and weak in contrast to silica hydrogel, and that theformer do not hold their form.

We have prepared zirconia hydrogels by the methods employed by Hurd eta1. and found that on attempting to wash the hydrogels with water atroom temperature they dissolved completely. It would seem that it isimpossible to prepare a dry zirconia gel by that method.

Notice may also be taken of the fact that plural oxide gels comprisingzirconia as a minor constituent may be prepared by formation of ahydrosol containing a major proportion of some other water insolubleinorganic oxide, for example silica.

It has been shown heretofore that zirconia is a valuable catalytic agentand component of catalytic compositions. For example, active catalystsfor cracking of hydrocarbons are prepared by forming compositions ofsilica and zirconia. According to one known method, silica gel isimpregnated with zirconium nitrate and ignited to decompose the metalsalt to zirconia. Molded mixtures of silica and zirconia precipitateshave also been suggested as hydrocarbon conversion catalysts. Resultsobtained by these methods of preparing petroleum conversion catalystsindicated that zirconia is a valuable constituent. However, impregnationis not fully satisfactory because of diiliculties in control; andprecipitates in general share the disadvantages of being soft and chalkyin structure and low in catalytic activity.

The present invention provides a method for the preparation of truehydrogels consisting of zirconia or comprising zirconia as the majorinorganic oxide constituent and of such stability that they may bewashed free of water soluble matter and dried to form extremely porous,hard, translucent and glassy masses. These may be used as such,impregnated with other oxides and the like, or milled with othersubstances. Preferably, milling is done before dehydration is complete;as by kneading washed wet zirconia gel with wet alkali-free silica gelin a ball mill to prepare the mixture for extrusion to pellets and thelike. In order to facilitate the molding of the composited gels, a minorportion of the gels may be added during the kneading operation in theform of a dry finely-divided powder.

These and other objects and advantages of the invention are obtained byreacting aqueous solutions of soluble zirconium compounds with watersoluble salts of weak acids, such as acetic, carbonic, lactic, oxalic,nitrous and sulfurous acids, to yield homogeneous zirconia hydrosolscontaining substantially no precipitate and preferably having a pH valueof about 1.5 to about 7; permitting the sol to gel and thereafterwashing the hydrogel with an aqueous medium preferably at temperaturesabove about C. until the gel is substantially free of water solublesaltsj. Washed zirconia hydrogel is stable in neutral solvents, butdissolves in acids and acidic salts, hence this fact must be taken intoaccount when converting the hydrogel into catalytic masses byimpregnation with desirable components by any means. For most purposes,drying -to yield a dry porous body is desired and this mayadvantageously be accomplished by removal of water at about to C. untilshrinkage of the gel due to removal of water has been completed,whereupon the zirconia gel is further dehydrated at about 300 C. Theterm weak acid" as used here has the connotation generally understood inthe art. It refers to acids having relatively low ionization constants,say, below 0.1, as contrasted with the strong mineral acids,hydrochloric, sulfuric. etc., which are substantially completely ionizedexcept in very concentrated solutions.

zirconia hydrogels prepared by reacting solutions of a zirconiumcompound and a salt or a weak acid may or may not be stable on standingat room temperature for long periods time. For example, a gel preparedfrom solutions of zirconyl chloride and ammonium carbonate is stable atroom temperature, while a gel from zirconyl chloride and ammoniumacetate reliquefled under the same conditions. Neither of these gels canbe washed at room temperature without complete or substantial solutionof zirconia: however, the loss of zirconia decreases with increase intemperature of the wash water, and at 60 C. or above there is no loss ofzirconia due to solutiOn in water.

zirconia hydrogels prepared from solutions of a zirconium compound andtwo or more salts of weak acids containing at least two different kindsof acid radicals are stable at room temperature and may be washed withwater at this temperature with only a little loss of zirconia. Since wehave found that there is no liquefaction of zirconia gel in water at 60C., and because in commercial practice it is undesirable to lose anyvaluable material which subsequently must be recovered, we prefer towash such hydrogels at temperatures above about 60 C.

The preferred method consists of dissolving solid ammonium carbonate ina solution of zirconyl chloride or zirconium nitrate while efiicientlymixing the solution so that the precipitate which forms dissolves.Ammonium carbonate is added to the point where further addition wouldresult in a precipitate which would not redissolve. The resultingsolution is mixed with a solution of ammonium acetate of suchconcentration and in such proportion that a zirconia sol forms having apH between 3.8 and 5.5. This sol on standing will set to a hydrogel; thetime of gelation depends upon the concentration, acidity andtemperature. All zirconia hydrogels prepared by this procedure retaintheir form and most of them are as flrm or firmer than silica hydrogels.These zirconia hydrogels when placed in water at room temperaturedisintegrate to form small fragments and may partially liquefy, however,at 60 C. or above, they are stable and may be washed free of solublesalts and dried.

Instead of reacting the zirconium compounds with ammonium carbonate andammonium acetate other soluble carbonates and acetates and salts of weakacids may be used, as for example, sodium carbonate; sodium acetate,potassium acetate, etc. Metal carbonates and metal acetates offer adisadvantage in that a more thorough washing of the hydrogels must beconducted, since the water soluble products formed are non-volatile.Residual ammonium held in the gel, probably zeolitically but not as asalt, is removed during drying as ammonia. zirconia hydrogels may bemanufactured by reacting water soluble zirconium compounds with eitherammonium carbonate or sodium acetate; these hydrogels liquefy to a largeextent when washed at room temperature, but are stable on washing above60 C. Hydrogels prepared from zirconyl chloride and sodium carbonate bythe Hurd et al. method are stable on standing at room temperature, butdissolve in water at any temperature and hence are of no value.

To summarize the characteristic behaviour of zirconia gels formed byreactions or water soluble salts of weak acids, it has been establishedthat stable hydrogels capable 01' being washed and dried may be preparedby observing certain basic considerations. If water soluble salts of twoor more weak acids are reacted with water soluble zirconium compounds toform a gel in which the major molar proportion of insoluble inorganicoxide is zirconia, the gel may be washed at varying temperatures,including room temperature and below. However, zirconia is dissolved tosome extent and lost by washing at the lower temperatures and we preferto wash at 60 C. or above. Stable gels in which zirconia constitutes themajor molar proportion of insoluble inorganic oxides may also beprepared by reaction of soluble zirconium compounds and a single watersoluble salt of a weak acid other than alkali metal carbonates, if thegel is washed at a temperature of at least about 60 0. As pointed outabove, no method is known to us for preparing stable zirconia hydrogelsif only alkali metal carbonates are used to form the gelable sol.However, mixtures of such carbonates with other salts of weak acidsyield gels which can be washed at room temperature and below, althoughsuch washing at low temperature does'result in some loss of zirconiafrom the gel.

In general, the alkali metal, ammonium and alkaline earth metal salts ofweak acids are considered more suitable for the purposes of theinvention, and of these the alkali metal and ammonium salts aregenerally more suitable for use in the invention. For many purposes,ammonium salts are best because ammonia can be driven from the gel as agas, eliminating the removal problem encountered with non-volatilemetals. For best results, pH value at the time of gelation should becorrelated to the salt or salts employed. For example, acetates arepreferably used at pH 1.5 to 5.5; ammonium carbonate is best used at pH1.5 to 3; and mixtures of acetates and carbonates are fully effectiveover the range pH 1.5 to 7.

It has been found that gels consisting of zirconia will decompose attemperatures below those at which many catalytic substances areemployed. As a general rule, gels consisting of zirconia will nottolerate temperatures above about 300 C. Commercial catalytic crackingoperations, however, normally involve temperatures of 400-500 C. Thisdefect can be largely overcome by the use of zirconia in combinationwith another inorganic oxide which acts to render the combination muchmore resistant to temperatures. Gels may be formed according to thisinvention containing silica, boric oxide, alumina or other waterinsoluble amphoteric oxide. Gels containing such other oxides insubstantial amounts are stable at higher temperatures and gels withinthe scope of the invention may be prepared which are suitable for use atthe temperatures involved in catalytic cracking and regeneration of thecatalyst.

In regard to time of gelation, it may be stated in general that the timeof gelation is a minimum at about pH 4.5. At constant pH, the gelationtime decreases with increasing concentration or with increasingtemperature. The most concentrated gels, hence, are prepared attemperaiusres below room temperature and at about pH The zirconiahydrogels prepared as described in Examples 1, l1, and III were washedat about 65 C. until substantially free of soluble salts, dried at aboutC. to constant weight and then dried at gradually-increasingtemperatures to 300 0., at which temperature the gels were maintainedfor five hours.

Example I Two hundred-fifty grams of solid ammonium carbonate were mixedwith five liters of a solution containing 1960 grams of ZIOC123H2O untilsolution was complete. This solution was cooled to about C. and thenstirred by means of an efllcient mechanical device while 3.75 liters of2.35 normal ammonium acetate were added. A colloidal solution ofzirconia formed which has a pH of 4.4 and set to a gel 90 seconds afterthe ammonium acetate solution was added. This hydrogel was stable onstanding at room temperature.

Example II To four liters of a solution containing 3,138 grams ofZrOCla-8Hz0 were added 5.76 liters of four normal sodium acetate whilethe former solution was stirred with an efflcient mechanical mixer. Bothsolutions were cooled to about 5 C. prior to mixing. The resulting 501had a pH of 4.3 and set to a gel in 38 seconds. This hydrogel wasunstable at room temperature, reliquefying after a, period of time;however, it was stable during the washing at 65 C. and after this, wasreadily dried without reliquefaction.

Example III A solution containing 784 grams of ZrOCl2-8H2O and 100 gramsof ammonium carbonate per liter was mixed in a mixing nozzle with aneight normal solution of ammonium acetate to form a sol, which wasextruded into a column of oil and thereby dispersed into globules whichset to a hydrogel in the oil. The hydrogel beads were conducted out ofthe bottom of the column in a stream of water and immediately placed inwater at 65 C. and washed. The two solutions were cooled to about 5 C.before mixing. They were mixed in the ratio of 1.00 volumes of zirconylchloride-ammonium carbonate solution to 0.370 volume of ammonium acetatesolution. The zirconia sol had a pH of 3.9 and a gelation time ofseconds.

The zirconia hydrogel prepared according to this example was stable atroom temperature, but not completely stable in water at roomtemperature; however, only a small amount of zirconia was lost bysolution as determined by washing a portion of this hydrogel with waterat room temperature.

Example IV A zirconia hydrogel was prepared according to Example I,using the same quantity of reagents as reported therein. The salt-freehydrogel was soaked in 590 cc. of ethyl silicate, diluted to 3.25 literswith 95% ethyl alcohol to give an approximate composition on the drybasis of 80% 2102, S102. After standing overnight, the ethyl silicatesolution was poured off and the hydrogel was covered with water andallowed to stand six hours at room temperature, then overnight at 160 F.After draining the impregnated hydrogel, it was dried at 180 F. untilshrinkage was substantially complete and then dried at a graduallyincreasing temperature to 11.00 F. The dry gel was tested as a crackingcatalyst in the form of 6-14 mesh size granules under standardconditions, which involved passing a fraction of Oklahoma City Gas Oilhaving a boiling range of 470 to 708 F. through the catalyst bed at aliquid space velocity of 1.5 for 20-minute periods be- 6 tweenregenerations and ata temperature of 800 1''. 57% or the oil charged wasconverted to gasoline having a 410 F. end point.

Example V resulted in a 42% conversion of gas oil to 410 F.

end point gasoline.

Example VI This illustration is similar to that of Example V, the onlymodification is the substitution of alkali-free silica-alumina hydrogelfor silica hydrogel. This silica-alumina hydrogel when converted to thedry gel gave a 24% conversion of gas oil to gasoline under standardconditions whereas the dry gel of this example (80% zirconia, 20%silica-alumina) yielded a, 44% conversion to gasoline.

Example VII The use of formates is typified by a gel produced by actionof ammonium formates. A sol was prepared by adding 13 grams of ammoniumformate to 100 cc. of an aqueous solution containing 39.2 gramsZrOCl2'8H2O and stirring until the precipitate dissolved. That so] wasmixed with an equal volume of 0.20 normal ammonium formate producing asol of pH 2.6 which set in 30 seconds at room temperature. The resultantgel was washed at 60-65 C. without appreciable losses.

Example VIII Sodium nitrite was added to the zirconyl chloride solutionof Example VII in the ratio of 5 grams of salt per 100 cc. of solution.A small amount of precipitate formed but re-dissolved on stirring. Onevolume of saturated sodium nitrite solution was added to live volumes ofthe sol and the mixture was found to have a pH of 3.3 and a setting timeof ten seconds at room temperature. The gel was washed and dried in thesame manner as in Example VII.

Example IX To 900 cc. of an aqueous solution containing 0.392 gramZlOC12'8H2O per cc. was added 45 grams of ammonium carbonate and thiswas then mixed with 557 cc. sodium silicate solution prepared bydilution of N brand water glass to 0.025

7 gram SiOz per cc. This was cooled to 0 C..

stirred with 198 cc. of eight normal ammonium acetate, also cooled to 0C. to give a sol having a pH of 4.5 which set in one minute. Thegelation time of this sol at room temperature is so short that eflicientmixing at room temperature is impossible. Satisfactory use of thetechnique of Example III is achieved by injecting the cold sol at 0 C.to an 011 column maintained at room temperature. The globules of sol areheated by the oil and thus caused to gel in a shorter time to firmhydrogel beads. In either case, the gel is washed at 60 to 65 0., driedovernight at C. and heat treated at 550 C. to prepare a catalyst for thecracking of hydrocarbon oils.

7 Example X It has been shown above that more stable gels may beproduced by reacting salts of two diflerent weak acids with a watersoluble zirconium compound in an aqueous solution. In general,substantially the same results may be attained by using an aqueous base,such as ammonia, sodium hydroxide, potassium hydroxide, etc., and awater soluble salt of a weak acid. In such cases, the aqueous base isadded to an aqueous solution of a water soluble zirconium compound andthe salt of a weak acid is then added to the solution to adjust the pHto a desired value.

Ammonia is added to a solution of zirconium chloride just until theprecipitate first formed no longer redissolves. Aqueous ammonium acetateis then added with efficient agitation in an amount sufllcient to adjustthe pH to 4.4. Gelation takes place within a relatively short time. Thisgel is washed at 60 to 65 C. and then dried in the usual mannerindicated above. The gel is characterized by a stability considerablybetter than that enjoyed by a gel prepared by the use of a single weakacid salt and is on the order of that obtained when salts of two weakacids are used.

Example XI To 2.00 liters of zirconyl chloride solution containing 1568grams ZrOClz-BHaO was added with vigorous stirring 3.40 liters of 3.47normal calcium acetate. Both solutions had previously been cooled toabout C. The hydrosol thus formed had a pH of 4.9 and set to a firm gelin 50 seconds. The hydrogei was washed (at 65 C.) and dried in the usualmanner to yield a hard, transparent product.

Example XII Eighty-five grams of solid sodium nitrite were mixed with1.00 liters of a solution containing 392 grams ZrOCh-8Hz0. This solutionwas cooled to 5' C. and then stirred vigorously while 0.400 liter of 4normal sodium nitrite were added. The hydrogel had a pH-of 3.6 and setto a gel in 35 seconds.

We claim:

1. A method for formation of zirconia-containing gels comprisingreacting in aqueous solution a water soluble zirconium compound andwater soluble salts of at least two weak acids to effect formation of ahomogeneous hydrosol in which zirconia is the major water insolubleinorganic oxide component and which has a pH value of about 4.5,permitting the said hydrosol to set forming a hydrogel containingzirconia and washing said hydrogel to remove water soluble saltstherefrom.

2. A method for formation of zirconia-containing gels comprisingreacting in aqueous solution a water soluble zirconium compound andwater soluble salts of acetic acid and at least one other weak acid toeffect formation of a homogeneous hydrosol in which zirconia is themajor water insoluble inorganic oxide component and which has a pH valuebetween about 1.5 and about 7.0, permitting the said hydrosol to setforming a hydrogel containing zirconia and washing said hydrogel toremove water soluble salts therefrom.

3. A method for formation of zirconia-containing gels comprisingreacting in aqueous solution a water soluble zirconium compound,ammonium acetate and a water soluble salt of at least one other weakacid to effect formation of a homogeneous hydrosol in which zirconia isthe major water insoluble inorganic oxide component and which has a pHvalue between about 1.5 and about 7.0, permitting the said hydrosol toset forming a hydrogel containing zirconia and washing said hydrogel toremove water soluble salts therefrom.

4. A method for formation of zirconia-containing gels comprisingreacting in aqueous solution a water soluble zirconium compound, a watersoluble ammonium salt of a weak acid and a water soluble salt of atleast one other weak acid to effect formation of a homogeneous hydrosolin which zirconia is the major water insoluble inorganic oxide componentand which has a pH value between about 1.5 and about 7.0, permitting thesaid hydrosol to set forming a hydrogel containing zirconia and washingsaid hydrogel to remove water soluble salts therefrom.

5. A method for formation of zirconia-containing gels comprisingreacting in aqueous solution zirconyl chloride and water soluble saltsof at least two weak acids to effect formation of a homogeneous hydrosolin which zirconia is the major water insoluble inorganic oxide componentand which has a pH value between about 1.5 and about 7.0, permitting thesaid hydrosol to set forming a hydrogel containing zirconia and washingsaid hydrogel to remove water soluble salts therefrom.

6. A method for formation of zirconia-containing gels comprisingreacting in aqueous solution zirconyl chloride, a water soluble ammoniumsalt of a weak acid and a water soluble salt of at least one other weakacid to effect formation of a homogeneous hydrosol in which zirconia isthe major water insoluble inorganic oxide component and which has a pHvalue between about 1.5 and about 7.0, permitting the said hydrosol toset forming a hydrogel containing zirconia and washing said hydrogel toremove water soluble salts therefrom.

7. A method for formation of zirconia-containing gels comprisingreacting in aqueous solution zirconyl chloride, ammonium acetate and aWater soluble salt of at least one other weak acid to effect formationof a homogeneous hydrosol in which zirconia is the major water insolubleinorganic oxide component and which has a pH value between about 1.5 andabout 7.0, permitting the said hydrosol to set forming a hydrogelcontaining zirconia and washing said hydrogel to remove water solublesalts therefrom.

8. A method for formation of zirconia-containing gels comprisingreacting in aqueous solution a water soluble zirconium compound andwater soluble salts of acetic acid and at least one other weak acid toeffect formation of a homogeneous hydrosol in which zirconia is themajor water insoluble inorganic oxide component and which has a pH valuebetween about 1.5 and about 7.0, permitting the said hydrosol to setforming a hydrogel containing zirconia and washing said hydrogel toremove water soluble salts therefrom, at a temperature not substantiallybelow about 60 C.

9. A method for formation of zirconia-containing gels comprisingreacting in aqueous solution a water soluble zirconium compound,ammonium acetate and a water soluble salt of at least one other weakacid to effect formation of a homogeneous hydrosol in which zirconia isthe major water insoluble inorganic oxide component and which has a pHvalue between about 1.5

a and about 7.0, permitting the said hydrosol to set forming a hydrogelcontaining zirconia and washing said hydrogel to remove water solublesalts therefrom, at a temperature not substantialiy below about 60 C.

10. A method for formation of zirconia-containing gels comprisingreacting in aqueous solution a water soluble zirconium compound, a watersoluble ammonium salt of a weak acid and a water soluble salt of atleast one other weak acid to eflect formation of a homogeneous hydrosolin which zirconia is the major water insoluble inorganic oxide componentand which has a pH value between about 1.5 and about 7.0, ermitting thesaid hydrosol to set forming a hydrogel containing zirconia and washingsaid hydrogel to remove water soluble salts therefrom, at a temperaturenot substantially below about 60 C.

11. A method for formation of zirconia gels comprising reacting inaqueous solution of a water soluble zirconium compound and water solublesalts of at least two weak acids to efiect formation of a homogeneoushydrosol in which zirconia is substantially the only water insolubleinorganic oxide and which has a pH value between about 1.5 and about7.0, permitting the said hydrosol to set forming a hydrogel of zirconia,washing said hydrogel to remove water soluble salts therefrom at atemperature not substantially below about 60 0., drying said washedhydrogel at about 75 to about 120 C. and thereafter dehydrating the sameat a temperature not substantially above about 300 C.

12. A method for formation of zirconia-containing gels comprisingreacting in aqueous solution zirconyl chloride and water-soluble saltsof at least two weak acids to effect formation of a homogeneous hydrosolin which zirconia is the major water-soluble inorganic oxide componentand which has a pH value between about 1.5 and about 7.0, permitting thesaid hydrosol to set forming a hydrogel containing zirconia and washingsaid hydrogel to remove water-soluble salts therefrom, at a temperaturenot substantially below about 60 C.

tion a water-soluble zirconium compound and 13. A method for formationof zirconia-coni taining gels comprising reacting in aqueous solutionzirconyl chloride and water-soluble salts of at least two weak acids toeffect formation of a homogeneous hydrosol in which zirconia is themajor water-insoluble 1 inorganic oxide component and which has a, pHvalue between about 1.5 and about 7.0, permitting the said hydrosol toset forming a hydrogei containing zirconia and washing said hydrogel toremove water-soluble salts therefrom, at a temperature not substantiallybelow about C., drying said washed hydrogel at about C. to about 120 C.and thereafter dehydrating the same at a temperature not substantiallyabove about 300 C.

14. A method for formation of zirconia-conwater-soluble salts of atleast two weak acids to effect formation of a homogeneous hydrosol inwhich zirconia. is the major water-insoluble inorganic oxide componentand which has a pH value between about 1.5 and about 7.0, permitting thesaid hydrosol to set forming a hydrogel containing zirconia and washingsaid hydrogel to remove water-soluble salts therefrom.

15. A stable inorganic oxide gel consisting of zirconia, capable ofbeing water-washed at room temperature without disintegration, whichresults from the reaction of a water soluble zirconium compound andwater-soluble salts of at least two weak acids to effect formation of agelable hydrosol of zirconia having a pH value between about 1.5 andabout 7.0, permitting the said hydrosol to set forming a hydrogel ofzirzonia and washing said hydrogel to remove watersoluble saltstherefrom.

16. A process for the conversion of hydrocarbons which comprisescontacting hydrocarbon vapor at conversion conditions of temperature andpressure with a catalyst consisting of silica impregnated zirconia gelprepared by a process comprising reacting in aqueous solution awatersoluble zirconium compound and water-soluble salts of at least twoweak acids to effect formation of a gelable hydrosol of zirconia havinga pH value between about 1.5 and about 7.0, permitting the said hydrosolto set forming a hydrogel consisting of zirconia, washing said hydrogeltoremove water-soluble salts therefrom, soaking the salt-free hydrogelin silicate solution to give an approximate composition on the dry basisof per cent zirconia and 20 per cent silica, removing the impregnatedhydrogel from the silicate solution, soaking said hydrogel in wateruntil substantially free of soluble salts, draining the washedimpregnated hydrogel and drying the same at an elevated temperature.

MILTON M. MARISIC. EDWARD M. GRIEST.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,289,918 Lee et al July 14, 19422,338,089 Bond, Jr Jan. 4, 1944 2,349,243 Bates May 23, 1944 2,378,904Bates June 26, 1945 OTHER REFERENCES Certificate of Correction PatentNo. 2,442,772. June 8, 1948.

MILTON M. MARISIC ET AL.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Column 9,line 39, claim 12, for water-soluble read water-insoluble; and that thesaid Letters Patent should be read with this correction therein that thesame may conform to the record of the case in the Patent Oflice.

Signed and sealed this 16th day of November, A. D. 1948.

[SEAL] THOMAS F. MURPHY,

Assistant Commissioner of Patents.

